1. Field of the Invention
The invention relates to a process and apparatus for facsimile coding in which items of information contained on a two-color original are scanned line-by-line for the purpose of transmission, in which the length of the sequences of a first of these colors is represented by first code words consisting of a given first number of binary characters and the length of sequences of a second color is represented by second code words consisting of a second number of binary characters, and in which the first and second code words are followed by at least one third code word when the binary characters are not sufficient for the coding of the corresponding sequences.
2. Description of the Prior Art
The publication by D. Preuss: Redundanzreduzierende Codierung von Faksimilesignalen, Nichrichtetechnische Zeitschrift (Redundancyreducing Coding of Facsimile Signals, Communications Technological Magazine), Vol. 11 (1971) Pages 564 to 568 discloses a process for coding the lengths of sequences of a first color and a second color in facsimile transmission, this process being referred to as sequence length coding. In this process the lines which are to be scanned are broken down into portions of like colors, of equal brightness, which are referred to as sequences. For each sequence, a code word is produced, which code word indicates the relevant number of image points, and which is referred to as sequence length, in the form of a dual number. If a code word is not adequate to represent a sequence length, it is supplemented by additional code words of equal length.
If a code word produced by this known process is transmitted in faulty fashion, the associated sequence length is incorrectly reproduced in the receiver and the entire following image content is displaced. A faulty transmission has particularly disadvantageous effects when a code word is supplemented by an additional code word in order to represent a long sequence, but this additional code word is not recognized. In this case the receiver can no longer correctly assign the received code words the sequence lengths for the first color or the second color, since it is no longer able to recognize which characters form a code word. If, however, a line synchronizing word is provided at the beginning of each line, the effects of a fault can be limited to one line.